1. Field of the Invention
This invention relates to a process for making expanded fried snack products from any of a number of combinations of dry starch-containing ingredients, including cereal flours, dried potatoes, etc.; and more particularly, to a process for reducing undesired "puffing" of an expanded snack during deep fat frying.
2. Description of the Prior Art
A variety of deep fat fried snacks are on the market today. These snack products are commonly made from a dough containing corn or potato solids. Typically, the dough is shaped or formed, such as by roller-forming or extrusion under high pressure, and the shaped or formed dough pieces are then deep fried to produce the finished expanded fried snack product. It has been widely recognized that the problem of "puffing" can occur in snack products made from a formed moist dough piece that is deep fat fried. Puffing commonly occurs because of the accumulation of steam between the outer surfaces of the dough piece during frying. This causes the sides of the dough piece to separate, forming bubbles (i.e., internal voids) or, when the bubbles rupture, exposed holes in the snack. Puffing detracts from the appearance of the snack, and when filled with excess fat, it greatly increases the fat content of the product. Separation of a dough piece in the fryer also has been referred to in the art as "pillowing" or "blistering", but the term "puffing" is used herein to describe each of these phenomena, generally.
There have been a number of prior art techniques devoted to reducing puffing in expanded fried snacks. U.S. Pat. No. 2,905,559 to Anderson et al describes an attempt to avoid puffing by perforating the dough sheet with spikes after discrete pieces are formed. In a related patent, U.S. Pat. No. 3,278,311 to Brown et al, partly cooked corn kernels are treated by cutting the kernels to a size range of 0.5 to 1.27 mm and plasticizing the cut particles to make a cohesive dough. The dough is then rolled into sheet form and the dough sheet is perforated prior to frying.
U.S. Pat. No. 3,886,291 to Willard discloses experiments illustrating the importance of proper ingredient selection to eliminate puffing in extruded products made from mixtures of dehydrated potatoes and various starches. Only products made from potato starch and tapioca starch were of acceptable quality. No attempts were made to control puffing in these experiments.
U.S. Pat. No. 2,916,378 to Kunce et al mentions that ordinary corn chips do not puff because they are coarsely ground so that the dough is "discontinued" and steam from moisture within the dough can readily escape from the surface during the frying process. The manufacture of corn chips is described in several patents, such as U.S. Pat. Nos. 2,002,053 to Doolin and 3,278,311 to Brown et al. Controlling the particle size of the ground corn is extremely difficult because of many critical process variables, including the size, age and moisture content of the dry corn kernels, variations in moisture content and thus the softness of the soaked, partially-cooked kernels, rate of feed to the grinder, adjustment of clearance between the rotating grinding wheels and the gradual wearing of the grinding wheels. As a result, controlling puffing in sheeted snacks made from corn processed in this manner by relying on the critical control of particle size in the dough is impractical. In the Kunce et al process the corn is finely ground and the corn-based dough has a smooth continuous surface which would ordinarily puff if fried with a 50% moisture content; but Kunce et al rapidly predry the formed corn snacks in a high-temperature oven to about 15% moisture prior to frying, which creates an acceptable texture of small surface blisters following frying.
U.S. Pat. No. 3,883,671 to Shatila describes a process in which formation of surface blisters or puffing is reduced by moistening the surfaces of the flat dough pieces with water after forming and before frying. The surfaces can be moistened by spraying, dipping, or steaming. The Shatila patent also refers to other methods known to reduce puffing or blistering in similar processes. These include reference to U.S. Pat. No. 3,608,474 to Liepa, in which potato-based dough pieces are confined within a mold to physically prevent large blisters from forming. Another prior art technique is to form dough pieces with a corrugated surface, which also tends to prevent blistering. A further technique involves forming the dough to very thin layers of about 0.4 mm thickness, since blistering is reduced with thinner dough pieces. Shatila U.S. Pat. No. 3,883,671 emphasizes the difficulty of consistently producing a snack product with a smooth, blister-free surface when the thickness is in the range 0.030 to 0.045 inch (0.76 to 1.1 mm).
Thus, the prior art has disclosed a number of attempts at solving the problem of puffing or blistering; but the prior art has not provided a method that successfully controls puffing to within acceptable limits independently of such factors as (1) the thickness of the dough pieces (i.e., for thicker dough pieces of about 1.0 mm thickness or more), (2) the moisture content of the dough (i.e., for a moisture content greater than about 40% to 50%), and (3) the particular ingredients contained in the dough, without requiring special equipment such as water-moistening apparatus, hightemperature ovens, dough perforating apparatus, corrugating apparatus, molds for confining the dough, etc.